Hot-melt adhesive

ABSTRACT

A hot-melt adhesive having a superior adhesiveness at high temperature, comprising 100 parts by weight of a thermoplastic substance composed essentially of ethylene-vinyl acetate copolymer and 10-200 parts by weight of an inorganic filler.

United States Patent Susuki et al. {4 1 Sept. 12, 1972 [S4] HOT-MELT ADHESIVE 2,375,786 5/1945 Haywood .23! 129 72 mentors: Mk 5 H T k mm 3,061,577 /1962 Pruett ..260/41 A l 1 an", 1 ,512, am m; 3,503,922 3/1910 Carton ..260/41 A Minor" on both f Tokyo, n 3,419,641 12/1968 Peterkin etal ..260I897 B fj 3,573,240 3/1971 Flanagan ..260/28.5 A

, 7 4 1971 F1 agan [73] Assignee: Lion Fat 81 Oil Co Ltd., Tokyo, 3 5 7 372 I an 260,28 5 A Japan OTHER PUBLICATIONS [22] Filed: Nov. 20, 1970 Du Pont, Electrochemical Dept., Technical Information, PL 14- 865, 8/1965. Appl' Skeist, Handbook of Adhesives, Reinhold Co., pages 189, 223 and 273 relied on. Foreign Application Priority pm Nov. 25, 1969 Japan ..44/9a9s7 Lkbma" Assistant Examiner-S. L. Fox $21 11.8. CI. .....260/27 EV, 260/285 AV, 260/41 R, w- Blanchard and Flynn 260/41 A [51] Int. Cl. ..C08ll 9/12, C081: 11/70. C08f /04 ABSTRACT [58] new sunk-260,285 A hot-melt adhesive having a superior adhesiveness at I 9 high temperature, comprising parts by weight of a thermoplastic substance composed essentially of [56] Reine CM ethylene-vinyl acetate copolymer and 10-200 parts by UNITED STATES PATENTS Wish! of an inorganic filler- 2,269,608 1/1942 Strieby ..23/ 129 7 Claims, No Drawings HUI-MELT ADHESIVE BACKGROUND OF THE INVENTION 1 Field of the Invention The present invention relates to a hot-melt adhesive which demonstrates tackiness or adhesiveness only when subjected to heating, and more particularly, it relates to a hot-melt adhesive comprising a thermoplastic substance composed essentially of ethylene-vinyl acetate copolymer and a large quantity of an inorganic filler kneaded with said substance, whereby it is possessed of an improved adhesiveness at high temperature.

2. Description of the Prior Art Polyolefin plastics such as polyethylene, polypropylene, etc. are so chemically stable and inactive that any conventional adhesive, solvent-type and pressure-sensitive type, can hardly display a satisfactory efficiency in bonding thereof. For the purpose of effecting the bonding of such polyolefin plastics, therefore, it is prevalent to employ a hot-melt adhesive of the same family as or similar to said plastics or a hotmelt adhesive comprising a copolymer of these plastics. Said hot-melt adhesive not only is quite suitable for the intended use but also has a variety of advantages such that, because of the thermoplasticity of the components thereof, the joint of the plastics bonded thereby is flexible and highly resistive to impact, and, if the occasion demands, even the plastics once bonded and solidified can be easily detached again by heating. On the other hand, however, it has such drawbacks that it is poor in the property of resisting thermal changes, so that, especially when subjected to a relatively high temperature, the joint of the plastics bonded thereby becomes softened, thereby causing the contact surfaces ttkslip with respect to each other or the plastics to come With a view to making up for the foregoing drawbacks of the hot-melt adhesive, there has been proposed a method of adding a thermo-setting resin having a high thermal resistance, such as phenol resin, epoxy resin, etc., to said hot-melt adhesive. But, according to this method, provision of a sufficient thermal resistance for the hot-melt adhesive requires the employment of a large quantity of a thermo-setting plastic which is accompanied with the defect that the aforesaid various advantages characterizing the hotmelt adhesive come to be sacrificed thereto. Consequently, it has not been practical, and, besides, the friction pull strength thereof has proved insufficient.

There has also been practiced a means of making up for the foregoing defect mixing a small quantity of an inorganic substance such as calcium carbonate, clay, talc, white lead, etc. But, this means has proved unsatisfactory from the viewpoint of the friction pull strength.

SUMMARY OF THE INVENTION The present invention is intended to eliminate the above-mentioned drawbacks in the prior art, and its object is to provide a hot-melt adhesive which is prepared without admixing any thermo-setting plastic, etc. and yet not only is possessed of a very stable adhesiveness almost invulnerable to a low temperature or a high temperature but also retains those various advantages peculiar to the hot-melt adhesive.

This object is achieved by mixing, through kneading, a large quantity of an inorganic filler with a thermoplastic substance composed essentially of an ethylene-vinyl acetate copolymer. The thermoplastic substance applicable to the present invention is a compound comprising an ethylene-vinyl acetate copolymer as the main component thereof together with such assistants as the fluidity improver, tackifier, etc. Mixing of the fluidity improver is for the purpose of improving the adhesiveness and controlling the fluidity of the adhesive. The fluidity improver applicable to the present invention includes, for instance, chlorinated paraffin, natural wax and synthetic wax. To give examples of the tackifier, there are refined rosin, ester gum, polyisobutylene, petroleum resin, cumarone resin, alkylphenolformaldehyde resin, etc., and these can be applied either individually or by combining several of them appropriately. The above-mentioned inorganic tiller functions not only to provide the adhesive with thermal resistance and burning resistance but also as a reinforcing agent. It includes such inorganic substances as calcium sulfite, magnesium silicate, silicon dioxide, etc., and these can be applied either individually or by combining several of them appropriately. Especially, calcium sulfite proves efl'ective.

The adhesive according to the present invention is obtained by kneading the aforesaid inorganic filler with a thermoplastic substance prepared by mixing parts by weight of an ethylene-vinyl acetate copolymer, l0-40 parts by weight of the fluidity improver and 30-200 parts by weight of the tackifier, at the rate of 10-200 parts by weight of the fon'ner per 100 parts by weight of the latter. (The optimum content of the inorganic filler is in the range of 20-40 parts by weight per l00 parts by weight of the thermoplastic substance.) in preparing this composition of the adhesive, in case the quantity of the fluidity improver mixed with l00 parts by weight of said ethylene-vinyl acetate copolymer exceeds 40 parts by weight, the resultant adhesive comes to have more fluidity than that required and its adhesiveness is impeded, while, in case said quantity is less than 10 parts by weight, mixing of the fluidity improver does not lead to any practical result. In case the quantity of the tackifier mixed in the composition is less than 30 parts by weight, the resultant adhesive is short of tackiness and fails to have a satisfactory adhesive property. Mixing of the tackifier in excess of 200 parts by weight is also undesirable as it will result in a defective adhesive. As for the quantity of the inorganic substance to be mixed with the thermoplastic substance, in case it is less than 10 parts by weight, it is infeasible to obtain the intended effect of the mixing, namely, thermal resistive strength of the thermoplastic substance, while, in case it exceeds 200 parts by weight, the thermoplastic substance develops a tendency of becoming fragile and comes to lack mechanical strength such as impact resistance, etc. The ethylene-vinyl acetate copolymer defined herein is not necessarily specified, but it is desirable that it contains vinyl acetate in the range of 5-95 Wt%, and preferably in the range of 10-50 M96 as in the case of the product of the Du Ponts process of manufacturing high-pressure polyethylene copolymer.

In this connection, it is to be noted that the hot-melt adhesive according to the present invention is particularly effective when applied to polyolefine resins, and yet it works effectively on other thermoplastic resins, thermo-setting resins as well as various synthetic substances prepared by utilizing the foregoing resins, such as synthetic leather, synthetic paper, synthetic wood, etc.

In addition, it is also applicable to such natural manufactures as glass, metal goods, leather, paper goods, fiber, wood, stone, etc.

Upon preparing a test piece consisting of a couple of polyethylene pieces bonded with the adhesive of the present invention (which composition is shown in Example l) on one hand and a comparative test piece consisting of the same polyethylene pieces as above bonded with an adhesive absolutely free of the inorganic filler, friction pull tests were conducted on both test pieces. The result were as shown in the following Table 1.

TABLE 1 Friction pull strength kg/ZSAmm wide Adhesive containing Adhesive free of Test temperature 40 parts by weight inorganic filler of CaSO, -20 C 6.0 7.0

TABLE 2 Friction pull strength kg/25.4mm wide CaSO, Content 20C 40C (part by 7.0 0.43

weight) As seen from the foregoing Table 2, in case the temperature was comparatively low, gradual increase in quantity of the inorganic filler resulted in little changes in the friction pull strength of the present adhesive, while in case the temperature was comparatively high, said strength of the adhesive not containing the inorpanic filler was remarkably poor, but it radically increased with the increase in quantity of said filler, thereby manifesting the effect of the inorganic filler mixed therein.

(Remark) The above-mentioned quantity of CaSO, in terms of part by weight indicates the mixing rate of CaSO, calculated by regarding the total quantity of a mixture comprising 100 parts by weight of an ethylene-vinyl acetate copolymer, 120 parts by weight of a refined rosin and 30 parts by weight of a chlorinated parafiin as 100 parts by weight.

PREFERRED EMBODIMENT OF THE INVENTION EXAMPLE 1 Composition:

ethylene-vinyl acetate copolyrner l00 pans by weight (trade name: EVAFLEX 150, manufactured by Mitsui Polychernical Co.) refined rosin I20 parts by weight chlorinated paraffin 30 parts by weight calcium sulfite 100 parts by weight age resister, etc. 20 parts by weight [2.64li-tert-butyl-p-cresol (DJ-LT), dioctyl phthalate (D.O.P.), white lead] An adhesive according to the above composition was applied to one piece each of a couple of pieces of polyethylene tape, polypropylene tape, cotton cloth and cardboard, sized 25.4mm wide and 304.8mm long respectively. On the other hand, another adhesive prepared by omitting calcium sulfite from the same composition for the purpose of comparison was applied to the other piece of said polyethylene tape, polypropylene tape, cotton cloth and cardboard, respectively. Subsequently, all of these pieces were subjected to l-angle friction pull test at 40C. Comparative results of the test were as shown in the following Table 3. In this connection, the friction pull strength is usually measured by stripping at the rate of mm/min or thereabout, but, in the present example, the measurement was performed under a mare severe condition, namely, by stripping at the rate of 20 mrn/min.

TABLE 3 Friction pull strength Kg(40C) Adhesive under the Comparative present invention adhesive polyethylene tape 3.4 0.43 polypropylene tape 3.3 0.45 cardboard 3.6 0.52 cotton cloth 3.2 0.4l

As seen from the foregoing Table 3, the present adhesive mixed with calcium sulfite displayed friction pull strength about 8-9 times as much as that of an adhesive free of calcium sulfite at a temperature of 40C, proving the remarkable effect of the inorganic filler.

EXAMPLE 2 (B.H.T., D.O.P., white lead) 5 COMPARATIVE EXAMPLE I Composition:

ethylene-vinyl copolymer 100 parts by weight (trade name: EVAFLEX 1S0) age resister, etc. (B.H.T., D.O.P, white lead) calcium sulfite 20 parts by weight 200 parts by weight EXAMPLE 4 Composition:

ethylene-vinyl acetate 70 parts by weight (trade name: EVAFLEX I50) ester gum(non-hydrogenated I20 pans by weight product) I30'F paraffin 30 parts by weight polyiscbutylene I5 parts by weight age resistor, etc. 20 parts by weight (Bl-LT, D.O.P, white lead) silicon dioxide I parts by weight EXAMPLE Composition:

ethylene-vinyl acetate copolymer 70 parts by weight (trade name: EVAFLEX 420) petroleum resin 120 parts by weight (trade name: PETROSIN", manufactured by Mitsui Poly Chemical Co.)

I30? paraffin 30 parts by weight polyisobutylene parts by weight (Bl-LT, D.0.P, white lead) calcium sultite I00 parts by weight Upon changing the material to undergo the application of the adhesive with respect to the foregoing Examples 2, 3, 4 and 5 as well as Comparative Example I and by applying the same method of test as in Example I, measurement of friction pull strength was con- As seen from the foregoing Table 4, the friction pull strength of an adhesive containing calcium sulfite, magnesium silicate or silicon dioxide at room temperature was less deteriorative compared with that containing calcium carbonate, and, even at a high temperature, it

was fairly remarkable. Examples wherein thermosetting resin was employed:

COMPARATIVE EXAMPLE 2 Composition:

ethylene-vinyl acetate copolymer I00 parts by weight (trade name: BVAFLEX I50) refined rosin I20 parts by weight chlorinated paraffin 30 parts by weight age resister, etc. 20 parts by weight (Bl-LT, D.0.P, white lead) phenol resin (thermo-setting) I00 parts by weight toluene 630 parts by weight An adhesive according to the above composition was applied to a polyethylene tape, and, after evaporating toluene, it was caused to adhere to said tape by means of thermal pressure. The friction pull strength was as shown in the following Table 5.

TABLE 5 Adhesive strength (kg/25.4mm wide) As seen from the foregoing Table 5, in case of an adhesive containing a thermo-setting resin shows a remarkable deterioration of the strength at room temperature.

What we claim is:

l. A hot-melt adhesive composition, consisting essentially of a mixture:

a. a thermoplastic substance consisting essentially of 100 parts by weight of ethylene-vinyl acetate copolymer, l0-40 parts by weight of a fluidity improver selected from the group consisting of chlorinated paraffin, natural wax, synthetic wax and mixtures thereof, and 30-200 parts by weight of tackifier selected from the group consisting of refined rosin, ester gum, polyisobutylene, petroleum resin, cumarone resin, alltylphenol-formaldehyde resin and mixtures thereof b. an inorganic filler selected from the group consisting of calcium sulfite, magnesium silicate, silicon dioxide and mixtures thereof;

said composition containing from 20-200 parts by weight of said filler (b) per I00 parts by weight of said thermoplastic substance (a).

2. An adhesive as defined in claim 1, wherein the quantity of said inorganic filler is in the range of 20-40 parts by weight.

3. An adhesive as defined in claim 1, wherein said inorganic filler is calcium sulfite.

4. An adhesive as defined in claim I, wherein the weight ratio of ethylene to vinyl acetate in said ethylene-vinyl acetate copolymer is in the range of 95:5-5:95.

5. An adhesive as defined in claim 4, wherein the weight ratio of ethylene to vinyl acetate in said ethylene-vinyl acetate copolymer is in the range of zl0-50z50.

6. An adhesive as defined in claim 1, wherein the content of said ethylene-vinyl acetate copolymer in said thermoplastic substanee is in the range of 20-50 Wt%.

7. An adhesive as defined in claim 6, wherein the content of said ethylene-vinyl acetate copolymer in said thermoplastic substance is in the range of 25-45 Wt'k.

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2. An adhesive as defined in claim 1, wherein the quantity of said inorganic filler is in the range of 20-40 parts by weight.
 3. An adhesive as defined in claim 1, wherein said inorganic filler is calcium sulfite.
 4. An adhesive as defined in claim 1, wherein the weight ratio of ethylene to vinyl acetate in said ethylene-vinyl acetate copolymer is in the range of 95:5-5:95.
 5. An adhesive as defined in claim 4, wherein the weight ratio of ethylene to vinyl acetate in said ethylene-vinyl acetate copolymer is in the range of 90:10-50:50.
 6. An adhesive as defined in claim 1, wherein the content of said ethylene-vinyl acetate copolymer in said thermoplastic substance is in the range of 20-50 Wt%.
 7. An adhesive as defined in claim 6, wherein the content of said ethylene-vinyl acetate copolymer in said thermoplastic substance is in the range of 25-45 Wt%. 